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Combustion dynamics in a lean premixed combustor with swirl forcing and fuel conditions

Okon, Aniekan 2017. Combustion dynamics in a lean premixed combustor with swirl forcing and fuel conditions. PhD Thesis, Cardiff University.
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Abstract

Fossil fuels still account for a large percentage of global energy demand according to available statistics. Natural gas is increasingly gaining the share of these fuels due to the retired coal and nuclear plants. The more stringent emission standards have also put natural gas ahead of other fuels as a result of its efficiency, cost, environmental attributes as well as the operational efficiency of the gas turbine, an engine that uses this fuel. A standard low emission combustion technique in gas turbines is the dry low NOx combustion, with lean fuel and fuel-air premixed upstream of the flame holder. However, this condition is highly susceptible to combustion instabilities characterised by large amplitude oscillations of the combustor’s acoustic modes excited by unsteady combustion processes. These pressure oscillations are detrimental both to the efficiency of performance as well as the hardware of the system. Although the processes and mechanisms that result in instabilities are well known, however, the current challenges facing gas turbine operators are the precise understanding of the operational conditions that cause combustion instabilities, accurate prediction of the instability modes and the control of the disturbances. In a bid to expand this knowledge frontier, this study uses a 100kW swirl premixed combustor to examine the evolution of the flow structures, its influence on the flame dynamics, in terms of heat release fluctuation and the overall effects on the pressure field, under different, swirl, fuel and external excitation conditions. The aim is to determine the operational conditions whose pressure oscillation is reduced to the barest minimum to keep the system in an excellent running condition. The results of this study are expected to contribute towards the design of a new control system to damp instabilities in gas turbines.

Item Type: Thesis (PhD)
Status: Unpublished
Schools: Engineering
Uncontrolled Keywords: Combustion Dynamics; Lean Premixed Combustion; Swirling Flows; Forced Flow Combustion; Flexible Fuel Combustion.
Date of First Compliant Deposit: 18 January 2018
Last Modified: 19 Jan 2018 11:17
URI: http://orca-mwe.cf.ac.uk/id/eprint/108265

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